<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <script type="module">
    import { reactive, effect } from './index.js'
    
     const product = reactive({
       name: 'iPhone',
       price: 5000,
       count: 3
     })
     let total = 0
     effect(() => {
       total = product.price * product.count
     })
     console.log(total)

     product.price = 4000
     console.log(total)

     product.count = 1
     console.log(total)
  </script>
</body>
</html>